Charm production in the forward region: constraints on the small-x gluon and backgrounds for neutrino astronomy

TL;DR

This paper presents perturbative QCD predictions for charm production in the forward region, validated with LHCb data, to better estimate neutrino backgrounds for astrophysical neutrino observations.

Contribution

It provides validated charm production predictions and constrains the small-x gluon PDF, reducing uncertainties in neutrino background estimates for neutrino astronomy.

Findings

Good agreement between theory and LHCb data at 7 TeV.

Reduced uncertainties in small-x gluon PDF.

Predictions for charm production at 13 TeV and neutrino flux estimates.

Abstract

The recent observation by the IceCube experiment of cosmic neutrinos at energies up to a few PeV heralds the beginning of neutrino astronomy. At such high energies, the conventional neutrino flux is suppressed and the prompt component from charm meson decays is expected to become the dominant background to astrophysical neutrinos. Charm production at high energies is however theoretically uncertain, both since the charm mass is at the boundary of applicability of perturbative QCD, and also because the calculations are sensitive to the poorly-known gluon PDF at small-x. In this work we provide detailed perturbative QCD predictions for charm and bottom production in the forward region, and validate them by comparing with recent data from the LHCb experiment at 7 TeV. Finding good agreement between data and theory, we use the LHCb measurements to constrain the small-x gluon PDF, achieving a substantial reduction in its uncertainties. Using these improved PDFs, we provide predictions for charm and bottom production at LHCb at 13 TeV, as well as for the ratio of cross-sections between 13 and 7 TeV. The same calculations are used to compute the energy distribution of neutrinos from charm decays in pA collisions, a key ingredient towards achieving a theoretically robust estimate of charm-induced backgrounds at neutrino telescopes.